Knitting machine tools to which the present invention relates, such as latch needles, bearded needles, compound needles, sinkers, and, in general, yarn handling devices for use in knitting machines, and especially high speed, for example circular knitting machines, have been proposed in which a shank has at least one butt and two guide portions which extend down to the lower regions of the shank. The shank defines an upper and lower edge, the upper and lower edge being formed in narrow ribs of only up to 1.1 mm height, coupled by the guide portions adjacent the ribs. The space between the ribs and guide portions form a window which, in order to reduce vibration of the needle in operation of the knitting machine, is filled with a vibration damping material, such as a plastic, aluminum or the like, securely connected to the shank.
The referenced U.S. Pat. Nos. 4,562,705 and 4,783,976 show ribs which are very thin, that is, have a maximum height of only 1.1 mm. These knitting needles, due to the thin ribs, are highly elastic. In operation, the butts of the needles are engaged with the cam race of the knitting machine to move the needles between projected and withdrawn positions. During such movements, the needles tend to vibrate. Vibration can be damped by filling a window between the ribs and guide portions with a vibration damping material. A suitable vibration damping material is a plastic such as polyamide, which is secured to the material of the shank along the edges. Placing such vibration damping material in the window permits increase of the operating speed and additionally improves the long-term strength and operating integrity of the knitting needle. Breakage of the ribs due to metal fatigue, or breakage of a needle hook due to transmitted vibration and subsequent metal fatigue, is effectively attenuated.
Other knitting machine needles or, in general, yarn handling devices were proposed in which a free space is placed adjacent the rib of a shank, that is, the guide portions of the shank are connected by only a single narrow rib, shown, for example, in FIGS. 4 to 8 of the referenced U.S. Pat. No. 4,562,705, or FIGS. 2 and 5 of the referenced U.S. Pat. No. 4,783,976. Such constructions have the advantage that the elasticity of the needle is very high, so that it is suitable for extremely high operating speed. The vibration filling material is, however, connected only at the guide portions and to the sole, highly flexible rib, so that the connection between the vibration filling material, typically plastic, and with the shaft, is highly stressed. Under severe operating conditions, and particularly during long operating periods, the connection between the vibration damping material and the adjacent holding portions of the needle may sever at various points. Consequently, the vibration damping fill may break out at various positions, or can become detached entirely. The vibration damping effect of the damping material thus is lost more or less. Metal fatigue may then result at the highly elastic needles, which may lead to operating malfunction.
FIGS. 1 to 3 of the referenced U.S. Pat. No. 4,562,705, and FIGS. 1, 3, 4, 6 and 7 of the referenced U.S. Pat. No. 4,783,976, illustrate highly elastic needles in which two ribs are provided, between which the vibration damping material is placed, entirely filling the window formed between the ribs and the adjacent guide portions of the shank. Since the window is entirely defined and surrounded by the ribs and by the guide portions, the vibration damping material can be secured along all sides, so that even after long operating time, partial or complete severing or break-out of the damping material from the needle will not generally occur. Yet, although this needle has the advantage of retaining the vibration damping material, the operating stresses placed on the needle when the butt is rapidly moved, cause the flexible ribs to be subjected to sudden impact which cannot be transferred to the ribs equally in form of transverse essentially attenuated bending oscillations. Such absorption of vibration, due to the impacts applied by the butt to obtain movement of the needle under control of the butt, can be accepted by the highly elastic knitting needles in which the space beneath or above the rib and the adjacent guide portions is open. When the window is completely surrounded, the second rib interferes with development of bending oscillations, even if only to a minor degree. It has been found that such needles with an entirely surrounded window space, and damping material located therein, can be operated only at somewhat lower operating speeds than those which have an open space adjacent the rib, although the danger of loss of damping material has been eliminated.